Disk drives are capable of storing large amounts of digital data in a relatively small area. Disk drives store information on one or more recording media, which conventionally take the form of circular storage disks (e.g. media) having a plurality of concentric circular recording tracks. A typical disk drive has one or more disks for storing information. This information is written to and read from the disks using read/write heads mounted on actuator arms that are moved from track to track across the surfaces of the disks by an actuator mechanism.
Generally, the disks are mounted on a spindle that is turned by a spindle motor to pass the surfaces of the disks under the read/write heads. The spindle motor generally includes a shaft mounted on a base plate and a hub, to which the spindle is attached, having a sleeve into which the shaft is inserted. Permanent magnets attached to the hub interact with a stator winding on the base plate to rotate the hub relative to the shaft. In order to facilitate rotation, one or more bearings are usually disposed between the hub and the shaft.
Over the years, storage density has tended to increase, and the size of the storage system has tended to decrease. This trend has lead to greater precision and lower tolerance in the manufacturing and operating of magnetic storage disks. For example, to achieve increased storage densities, the read/write heads must be placed increasingly close to the surface of the storage disk. This proximity requires that the disk rotate substantially in a single plane. A slight wobble or run-out in disk rotation can cause the surface of the disk to contact the read/write heads. This is known as a “crash” and can damage the read/write heads and surface of the storage disk, resulting is loss of data.
From the foregoing discussion, it can be seen that the bearing assembly that supports the storage disk is of critical importance. One typical bearing assembly comprises ball bearings supported between a pair of races that allow a hub of a storage disk to rotate relative to a fixed member. However, ball bearing assemblies have many mechanical problems, such as wear, run-out and manufacturing difficulties. Moreover, resistance to operating shock and vibration is poor because of low damping.
One alternative bearing design is a hydrodynamic bearing. In a hydrodynamic bearing, a lubricating fluid such as oil provides a bearing surface between a fixed member of the housing and a rotating member of the disk hub. Hydrodynamic bearings spread the bearing surface over a large surface area, as opposed to a ball bearing assembly, which comprises a series of point interfaces. This is desirable because the increased bearing surface reduces wobble or run-out between the rotating and fixed members. Further, the use of fluid in the interface area imparts damping effects to the bearing, which helps to reduce non-repeat run-out.
A traditional design in the field of hydrodynamic bearing motors is the “single plate” design, in which axial stiffness is provided by two equally opposing thrust bearings positioned on the motor's shaft, and the bearing lubricant is retained by closing one bearing end and placing a capillary seal at the opposing end. This motor design is desirable for its improved angular stiffness and dynamic performance; however, manufacturing can be costly.
Therefore, a need exists for a single plate hydrodynamic bearing motor that can be manufactured at a low cost.